The language of the payment screen automatically matches the language of the internet browser. Suppose the language of the browser is set to German, then the text will also be in German.
The currently available languages are Dutch, English, (Belgian) French and German. It is also possible to 'force' the language, so that you decide what language is to be used. You then add a locale during the creation of the payment. You can find out how this works in our API-documentation.
If you decide not to use the locale option, and the consumer's browser language is not recognized, the text is rendered in English.